Screw machine having a plurality of symmetrically arranged rotors

ABSTRACT

The screw machine comprises consecutively mounted screw mechanisms (6, 7 and 8, 9) incorporating coaxially arranged stators (10, 12 and 14, 16) and rotors (11, 13 and 15, 17) disposed therein whose axes are offset with respect to the central axis of the stators (10, 12 and 14, 16) by the amount of eccentricity &#34;e&#34; of the screw mechanisms (6, 7 and 8, 9). The screw mechanisms (6, 7 and 8, 9) are grouped into modules (4, and 5) and the modules proper are grouped into blocks (3). The axes of the rotors (11, 13, 15, 17) of the screw mechanisms (6, 7 and 8, 9) in the module (4 and 5) and the modules (4, and 5) proper in the block (3) are arranged symmetrically relative to the central axis.

TECHNICAL FIELD

The invention relates to power engineering and, more particularly, toscrew machines.

PRIOR ART

Today, two basically different methods are used for drilling wells. Thefirst one is a rotor method of drilling whereby the drive of arock-breaking tool-bit is arranged on the surface and rotation to thebit is effected via a drill pipe string. The second method provides forthe use of downhole motors as a drive which are disposed directly abovethe bit. The drill pipe string is stationary. The second methodpossesses a whole number of obvious advantages: no power is needed torotate the drill pipe string, loads on drill pipes are diminished and,as a result, the number of failures in the borehole is decreased.

Among all types of downhole motors currently used in drilling wells,screw downhole motors are gaining a broad acceptance. These motors aresimple to operate and service, have small overall dimensions, enable oneto work with drilling muds of different density and viscosity (cf. M. T.Gusman, D. F. Baldenko et al. "Downhole Screw Motors for DrillingWells", Nedra Publishers, Moscow, 1981).

In their typical design these motors contain a housing, an output shaftwith radial and axial bearings and a screw mechanism which comprises astator with internal screw teeth and a rotor disposed therein withexternal screw teeth. The stator is made in the form of a metal housingwith an elastic lining vulcanized to its internal surface. In turn, theinternal surface of the elastic lining has screw teeth. The number ofthe stator teeth exceeds by one that of the rotor teeth therebyensuring, as the teeth interact, the division of the internal cavity ofthe screw mechanism into the working chambers--the cavities of high andlow pressure. As the working agent is pumped through the screwmechanism, the working members begin to move relative to one anotherunder the action of an arising pressure drop. In a typical most accepteddesign of the motor the stator is motionless and the rotor executes aplanetary motion- the rotor axis describes a circumference around thestator axis and the rotor proper rotates about its own axis. Thisrotation is transmitted to the motor output shaft. By changing thenumber and the length of the pitch of screw teeth, one may obtain anynecessary output characteristics of the motor. The latter is operated bythe flow of the working agent which may be liquid (water or drillingmud), as well as aerated fluid or compressed air.

The major disadvantage of the aforelisted motors is a strong transversevibration arising due to a specific motion of the screw mechanism rotor.Vibration causes a premature failure of the screw mechanism, the axialsupports of the motor and may lead to a breakdown.

Also known in the art is a screw downhole motor, which comprisessuccessively arranged screw mechanisms including coaxially disposedstators and rotors mounted therein whose axes are displaced relative tothe axes of the stators to the value of eccentricity "e" of the screwmechanisms, as well as a spindle section (USSR Inventor's CertificateNo. 286502, cl. F04 C5/00, 1969). This motor is basically the closestone to the present invention. In this design by way of calculations andselection of the lengths of coupling thread bushings, the axes of therotors disposed in two adjacent stators of the screw mechanisms may belocated in the same diameter to different sides from the axes of thestators. This assembly of the motor is fairly complicated and takes muchtime. Besides, an insignificant variation of the axial length of a groupof rotors or stators with respect to each other upsets the position ofthe axes of the rotors relative to one another which is establishedduring the assembly. A mere connection of one screw mechanism to anotherdoes not guarantee such an assembly. At the same time, the level ofvibrations in the outlined construction does not decrease even in caseof an optimal assembly because the forces of inertia and moments thereofaffecting the motor are not balanced out.

DISCLOSURE OF THE INVENTION

This invention is aimed at solving the problem of providing such a screwmachine the construction of which would allow of a substantial decreasein the impact of transverse vibrations on its units.

The problem set is solved owing to the fact that in a screw machinehaving successively disposed screw mechanisms which comprise coaxiallyarranged stators and rotors mounted therein whose axes are offsetrelative to the central axis of the stators by the amount ofeccentricity "e" of the screw mechanisms, according to the invention,the screw mechanisms are grouped into modules and the modules proper aregrouped into blocks, while the axes of the rotors of the screwmechanisms in the module and the modules proper in the block arearranged symmetrically relative to the central axis.

The disclosed construction of the screw machine makes it possible tosubstantially increase the service life of the machine and unitsthereof.

The service life is prolonged by reducing the effect of inertia andmoments thereof causing vibration. The symmetrical position of thevectors of the forces of inertia about the central axis of the statorsgives rise to the fact that the sum of all the forces of inertia actingin the machine is equal to zero. In most embodiments the symmetricalarrangement of the rotors serves to balance out the moments from saidforces of inertia.

It is preferred that the distance between the axes of the rotors of theadjacent screw mechanisms be equal. This is accomplished by successivedisplacement of the axis of the rotor in each subsequent screw mechanismrelative to the axis of the rotor of a preceding screw mechanism througha respective angle around the circumference of radius e equal to theeccentricity of screw mechanisms, with the centre coinciding with thecentral axis of the screw machine.

Such arrangement of the axis of rotors enables one to prolong stillfurther the service life of the machine not only owing to the balancingof the forces of inertia, but also thanks to a complete balancing ofmoments thereof.

In a preferred embodiment of the invention provision is made for guideunits adapted to ensure a preset relative displacement of the axes ofthe rotors and arranged in each block and in each module between therotors of screw mechanisms. The availability of the guide units enablesone to better preserve the preset orientation of the rotors of the screwmechanisms.

It is most expedient that each guide unit be made as a crank connectedwith the adjacent rotors by means of bearings, the axis of each bearingcoinciding with that of a respective rotor. Such structural embodimentof the guide unit makes it possible to streamline the assembly of thescrew machine.

The central angle of a symmetrical displacement of the axis of the rotorin each subsequent screw mechanism relative to the axis of the rotor inthe preceding screw mechanism depends on the number of screw mechanismsin the module. Likewise, the angle of turn of one module with respectito another depends upon the amount of modules in the block.

Depending on the number of screw mechanisms in each individual module,as well as depending on the number of individual modules in the block,one may substantially decrease, and in most variants of embodiment,completely balance the forces of inertia and moments thereof which helpsreduce the level of vibration of stators thread bushings and otherelements of the machine.

The reduction in the level of vibration of the screw machine improvesthe quality of a borehole drilling when using the screw machine as adownhole motor and stabilizes the operating conditions thereof.

The use of the guide units enhancing the reliability of orientation ofthe rotors in the screw mechanisms rules out the utilization ofadditional technological steps during the assembly of the motor whichare necessary in case the guide units are not available.

The use of cranks as guide units substantially streamlines the assemblyand cuts down the assembly time.

SUMMARY OF THE DRAWINGS

Other objects and advantages of the present invention will become moreapparent upon considering the following detailed description of theexemplary embodiments thereof, with references to the accompanyingdrawings in which:

FIGS. 1, 1a is the general view of the screw downhole motor,longitudinal section;

FIG. 2 is the cross section taken along II--II as in FIG. 1;

FIG. 3 is the cross section taken along III--III as in FIG. 1;

FIG. 4 is a variant of the connection of rotors in the screw mechanisms;

FIG. 5 is a diagram of the block of the screw machine, consisting ofthree modules, each comprising two consecutively arranged screwmechanisms;

FIG. 6 is a diagram of the arrangement of rotors in the modules of thescrew machine as in FIG. 5;

FIG. 7 is a diagram of the rotors in the block of the screw machine asin FIG. 5;

FIG. 8 is a diagram of the action of the forces of inertia in the screwmachine, as in FIG. 5;

FIG. 9 is a diagram of the block of the screw machine consisting of twomodules, each comprising threee consecutively arranged screw mechanisms;

FIG. 10 is a diagram of the arrangement of rotors in the screw machinemodule as in FIG. 9;

FIG. 11 is a diagram of the arrangement of the rotors in the block ofthe screw machine as in FIG. 9;

FIG. 12 is a diagram of the action of the forces of inertia in the screwmachine as in FIG. 9;

FIG. 13 is the general view of the screw machine used as a pump,longitudinal section;

FIG. 14 is the general view of the screw machine used as a compressor,longitudinal section.

BEST MODE FOR CARRYING OUT THE INVENTION

The screw machine in the variant of its embodiment as a downhole motorcomprises an actuating mechanism 1 (FIG. 1a, 1a*) and a bearing unit 2.In the given structural embodiment the actuating mechanism 1 includesone block 3 which has modules 4 and 5. The amount of blocks 3 in thescrew machine is determined by its output parameters (the torque,rotational speed, pressure drop) and, if necessary, may be increased.

The module 4 comprises two consecutively arranged screw mechanisms 6 and7; the module 5 contains, respectively, screw mechanisms 8 and 9.

Each of screw mechanisms 6, 7, 8, 9 contains a stator and a rotorarranged thereinside; for the screw mechanism 6--a stator 10 and a rotor11; for the mechanism 7--a stator 12 and a rotor 13; for the mechanism8--a stator 14 and a rotor 15; for the mechanism 9--a stator 16 and arotor 17.

The stators 10, 12, 14 and 16 of the actuating mechanism 1 and thebearing unit 2 are connected to each other by means of thread bushings18 and have a common central axis 00 coinciding with the axis of thescrew motor. The axes of rotors 11, 13, 15 and 17 are offset relative tothis common axis 00 by the amount of eccentricity "e". The rotor 17 isconnected to a shaft 19 of the bearing unit 2 with the aid of a flexibleshaft 20. The axis of the shaft 19 also coincides with the axis 00. Arock-breaking tool (not shown in FIG. 1a, 1a*) is secured to the outputend of the shaft 19.

In each screw mechanism 6, 7, 8 and 9 the interacting rotors 11, 13, 15and 17 the stators 10, 12, 14 and 16 corresponding thereto form workingchambers A dividing the inner cavities of the screw mechanisms 6, 7, 8and 9 into the cavities of high and low pressure.

The rotors 11 and 13, 13 and 15, 15 and 17 are interconnected by meansof flexible shafts 21, 22 and 23, respectively, owing to which axialforce from one rotor is transmitted to another (from 11, 13 and 15 to13, 15 and 17, respectively), as well as the greater portion of thetorque is transmitted. The connection of the rotors 11, 13, 15, 17 withthe flexible shafts 21, 22, 23 is effected in the form of smooth taperedsurfaces 24.

Besides, the rotors 11 and 13, 13 and 15, 15 and 17 are interconnectedby means of guide units 25 to ensure a symmetrical displacement of theiraxes. They also transmit a certain remaining portion of the torque. Theaxes of the rotors 11, 13, 15 and 17 displace with respect to oneanother around the circumference of radius "e" equalling the amount ofthe eccentricity of the screw mechanisms, with the centre coincidingwith the central axis 00. In the given variant the guide units 25 aremade in the form of cranks 26, 27 and 28 whose working surfaces 29 and30 are arranged in the respective rotors 11, 13, 15 and 17 by means ofbearings 31 and 32, thereby ensuring the rotation of the cranks 26, 27,28 relative to the rotors 11, 13, 15, 17 with a simultaneoustransmission of certain part of the torque.

The structural variant, wherein the crank 26 is arranged inside theflexible shaft 21 and the rotors 11 and 13 are interconnected via theflexible shaft 21 along the smooth tapered surfaces 24, to transmit theaxial force torque and ensures arrangement of the axes of the rotors 11and 13 relative to the common central axis 00 of the stators 10 and 12,the arrangement being preset by the crank 26.

The preset arrangement of the axes of the rotors 15 and 17 with respectto the common central axis 00 of the stators 14 and 16 is ensured in asimilar way with the aid of a crank 28 mounted inside the flexible shaft23.

Thus, the axes of the rotors 11, 13, 15 and 17 of the screw mechanisms6, 7, 8 and 9 are symmetrically oriented in the modules 4 and 5,respectively.

The modules 4, 5 proper are also symmetrically oriented relative to eachother by means of a similar guide unit 25 of the crank 27 mountedbetween the rotors 13 and 15 and arranged inside the flexible shaft 22which is also connected to the rotors 13 and 15 along the smooth taperedsurfaces 24.

In this case the central angle of the symmetrical location of the axesof the rotors 11, 13 and 15, 17 of the screw mechanisms 6, 7 and 8, 9 inthe modules 4, 5, respectively, being away from the central axis 00 bythe amount of eccentricity "e", depends on the basis of the total amountof the screw mechanisms in each individual module. The angle of asymmetrical displacement of the modules 4 and 5 proper in the block 3also depends on the number of modules in the block and is determined bythe arrangement of the axes of corresponding extreme rotors (11 and 15or 13 and 17).

As is clear from the consideration of the cross sections shown in FIGS.2 and 3, the axes of the rotors 11 and 13 of the preceding screwmechanism 6 and subsequent screw mechanisms 7 are displaced with respectto the common central axis 00 of the module 4 by the amount ofeccentricity "e" and occupy a diametrically opposite symmetricalposition.

FIG. 4 shows a structural variant of connecting the rotors 33 and 34 ofthe two consecutively arranged screw mechanisms 35 and 36. In the givenvariant the flexible shaft 37 is disposed inside the crank 38. Like inthe structure outlined above, the working surfaces 39 of the crank 38are arranged in the bearings 40 at the end portions of the connectedrotors 33 and 34 with the possibility of rotation. Stators 41 and 42 ofthe screw mechanisms 35 and 36 are connected to each other by a threadbushing 43 and together with the rotors 33 and 34 arranged inside form amodule 44.

The diagram of the screw machine shown in FIG. 5 comprises three modules45, 46 and 47, each consisting of two screw mechanisms, namely, 48 and49, 50 and 51, 52 and 53, respectively. The connection of rotors 54 and55, 56 and 57, 58 and 59 of said screw mechanisms 48, 49, 50, 51, 52, 53and their orientation, as well as the connection of rotors 54, 55, 56,57, 58, 59 of the adjacent modules 45, 46, 47 are effected by means ofthe flexible shafts 20, 21, 22, 23 and the guide units 25 according toone of the variants outlined hereinabove.

A symmetrical orientation of the axes of the rotors 54, 55, 56, 57, 58,59 in each individual module 45, 46, 47 is attained by their consecutivedisplacement relative to one another through an angle α=180°, becauseeach module 45, 46, 47 contains two screw mechanisms 48, 49, 50, 51, 52,53 (FIG. 6).

A symmetrical orientation of the modules 45, 46 and 47 proper (FIG. 7),which equals three in a block 60, is attained by displacing the axis ofthe rotor 56 of the screw mechanism 50 of the module 46 relative to theaxis of the rotors 54 of the screw mechanism 48 of the module through anangle β=120°, because the number of modules 45, 46, 47 in the block 60is three. The axis of the rotor 58 of the screw mechanisms 52 of themodule 47 is displaced analogously and in the same direction relative tothe axis of the rotor 56 of the screw mechanism 50 of the module 46. Theaxes of the rotors 54, 55, 56, 57, 58, 59 of the screw mechanisms 48,49, 50, 51, 52, 53 are displaced around the circumference of radius "e"equalling the amount of eccentricity of the screw mechanisms 48, 49, 50,51, 52, 53 identical for all mechanisms 48, 49, 50, 51, 52, 53.

FIG. 8 shows the diagram of the action of the forces of inertia in thescrew machine. The values of the forces of inertia F_(j54), and F_(j55),F_(j56) and F_(j57), F_(j58) and F_(j59) are equal and are also oppositein direction in pairs which ensures a complete balancing of not only theforces of inertia, but also the moments thereof. This is achieved byarranging the axes of the rotors 54, 55, 56, 57, 58 and 59 symmetricallywith respect to the central axis 00 of the screw machine, and making thedistances between the axes of the rotors 54 and 55, 56 and 57, 58 and 59equal.

A block 61 of the screw machine (FIG. 9) comprises two modules 62 and63, each consisting of three screw mechanisms 64, 65, 66, 67, 68, 69,respectively. Inside the module 62 (FIG. 10) the axes of rotors 70, 71and 72 of the screw mechanisms 64, 65 and 66 are consecutively displacedwith respect to one another through an angle α=120°, and therefore, thedistance between the axes of the rotors 70, 71 and 72 are the same. Theaxes of rotors 73, 74 and 75 of the screw 67, 68 and 69 are displaced inthe module 63 in an analogous manner.

The modules 62 and 63 proper (FIG. 11) are oriented to each other sothat the angle between the axes of the rotor 70 of the screw mechanisms64 in the module 62 and the rotor 73 of the screw mechanism 67 in themodule 63 is β=180°.

The axes of the rotors 70, 71 and 72 displace symmetrically as in thevariant described hereinabove along the circumference of radious "e",equalling the value of eccentricity of the screw mechanisms 64, 65, 66,67, 68, 69 which is the same for all mechanisms. The centre of thiscircumference coincides with the central axis 00 of the screw machineand all screw mechanisms 64, 65, 66, 67, 68, 69. The diagram of actionof the forces of inertia in the screw machine under consideration isshown in FIG. 12. In value determined by the mass of the rotors 70, 71,72, 73, 74 and 75, they are equal. In each separate module 62, 63 theforces of inertia (F_(j70), F_(j71), F_(j72) in the module 62 andF_(j73), F_(j74) and F_(j75) in the module 63) are completely balanced,because their sum is zero. Also completely balanced are the moments ofthe forces of inertia owing to the fact that the axes of the rotors 70,71, 72, 73, 74 and 75 are arranged symmetrically relative to the centralaxis 00 of the screw machine, and the distances between the axes of therotors 70, 71 and 72 in the module 62 and rotors 73, 74 and 75 in themodule 63 are equal.

FIG. 13 shows the screw machine according to the invention, which isused as a pump. Arranged in a housing of the pump is a bearing unit 77and a drive shaft 78 which via an articulated joint 79 is connected to arotor 80 of a screw mechanism 81. The rotor 80 is disposed inside astator 82 which is rigidly connected to the housing 76 of the pump.Stators 82, 83, 84 and 85 are connected coaxially to one another withthe aid of thread bushings 86. To ensure the transmission of the axialhydraulic load and the torque, as well as to ensure the presetdisplacement of the axes of the rotors 80, 87, 88 and 89, the latter areconnected to one another according to one of the aforelisted variants,namely, with the aid of flexible shafts 90 and guide units 91 made inthe form of a crank 92. The guide units 91 are arranged in respectiverotors 80, 87, 88, 89 by means of bearings 93 with the possibility ofrotation.

The stators 82, 83, 84 and 85 and the rotors 80, 87, 88 and 89respectively disposed therein, form the screw mechanisms 81, 94, 95 and96 assembled in pairs in modules 97 and 98 which in the given variantform only one block 99 of an actuating mechanism 100.

The pump has an input cavity B and output cavity C through which aworking liquid or another fluid medium is discharged.

The screw machine shown in FIG. 14 is used as a compressor, in the body101 of the compressor there is disposed an actuating mechanism 102including a block 103 of screw mechanisms 104, 105, 106 and 107. Thescrew mechanisms 104 and 105, 106 and 107 are united in pairs intoblocks 108 and 109, respectively. Stators 110, 111, 112 and 113 of thescrew mechanisms 104, 105, 106 and 107 are coaxially connected to eachother by means of thread bushings 114. Rotors 115, 116, 117 and 118 ofthese screw mechanisms 104, 105, 106, 107 are connected to one anotheraccording to one of the diagrams outlined hereinabove by means offlexible shafts 119 and guide units 120 made in the form of cranks 121with the aim of ensuring the transmission of the axial hydraulic loadand the torque, as well as providing a preset displacement of the axesof said rotors 115, 116, 117 and 118. A crank 121 is arranged inrespective rotors 115, 116, 117, 118 by means of bearings 112 with thepossibility of rotation.

The extreme rotor 118 of the screw mechanism 107 is rigidly connected toan articulated joint 123, and that one--to a drive shaft 124. Thearticulated joint 123 and the drive shaft 124 are disposed in a bearingunit 125 rigidly linked with the housing 101 inside which there arearranged cooling cavities D. The compressor has an input cavity E and anoutput cavity F through which gas medium is supplied to and discharged.

The screw machine in the variant of embodiment thereof is a downholemotor for drilling wells operates as follows.

From the drill pipes (not shown in FIG. 1) working fluid is fed to theworking chambers A of the first screw mechanism 6. Under action of apressure drop an active torque develops on the rotor 11 and the latterstarts rotating. From the rotor 11 rotation is consecutively transmittedvia the flexible shafts 21, 22 and 23 to the rotors 13, 15 and 17 andfurther to the bearing unit 2 unit 2 and then to the rock-breaking tool(not shown). The torques arising under the action of the pressure dropon the rotors 11, 13, 15 and 17 are summed up and are also transmittedvia the shaft 19 of the bearing unit 2 to the rock-breaking tool.

Having passed the working chambers A of the screw mechanism 6, theworking fluid enters the working chambers A of the screw mechanism 7.The pressure drop occurring in the working chambers A of this screwmechanism 7 creates an additional torque in the rotor 13. Thus, theworking fluid consecutively passes through the working chambers A of allscrew mechanisms 8, 9 and via the bearing unit 2 to the rock-breakingtool through which it gets to the well bottom.

The operating principle of the screw machine shown in FIGS. 13 and 14has the only distinction which consists in that the rotors 80, 87, 88and 89, 115, 116, 117 and 118 are driven by means of a motor (not shownin the drawing) via the drive shafts 78, 124, and the working fluid (gasmedium) is pumped over from the cavity B (E) via the working chambers Aof the screw machanisms 81, 94, 95, 96, 104, 105, 106, 107 to thecavities C (F).

INDUSTRIAL APPLICABILITY

The present invention can most effectively be used as a drive for arock-breaking tool in drilling oil and gas wells.

The invention can be used also as a downhole pumping unit for extractingwater, oil or other mineral resources which are pumped over in a liquidform.

Besides, the invention can be used in developing reliable pumping unitsor packaged compressors pumping over liquid, gaseous or mixed agents.

We claim:
 1. A screw machine which comprises consecutively mounted screwmechanisms comprising a plurality of coaxially arranged stators androtors disposed therein, the axis of the rotor is offset relative to theaxis of the stator within which it is disposed, by the amount ofeccentricity, "e", of the screw mechanism, wherein all of the statorshave a common axis and wherein the screw mechanisms are grouped intomodules each comprising at least two mechanisms and the modules aregrouped into blocks each comprising at least two modules, the axes ofthe rotors of the screw mechanisms forming the modules and axes of therotors of the screw mechanisms of the modules forming the blocks arearranged symmetrically with respect to the common axis about acircumference of radius "e" from said common axis, and the distancebetween axes of the rotors in adjacent screw mechanisms in each moduleare the same.
 2. A screw machine according to claim 1 wherein a guideunit is provided between the rotors of the screw mechanism in eachmodule and between the screw mechanism in each block.
 3. A screwmechanism of claim 2, wherein the guide unit is in the form of a bearingmounted crank connecting adjacent rotors, the axis of the bearingscoinciding with the axis of a respective rotor.